Squeegee and flood bar actuator with peeling screen clamp

ABSTRACT

The squeegee and flood bar assemblies of a screen printing machine are reciprocally moved along a spaced pair of parallel rails to alternately effect a printing stroke and a flood stroke. The rails are part of a frame which is pivoted for tilting movement between a printing position and a flood position. The squeegee assembly is slideably engaged in a third rail or control rail which is raised and lowered in coordination with the movement of the frame to lower the squeegee into contact with the printing screen at the start of the printing stroke and to raise it above the screen at the start of the flood stroke. The flood bar assembly is linked to the squeegee assembly to raise the flood bar when the squeegee is lowered and to lower the flood bar when the squeegee is raised. The front end of the printing screen is held in a clamp which is suspended below the parallel rails and includes a rod rotatably attached to the frame along an axis which is transverse to the rails, a pair of spaced lever arms projecting from the rod, and a linear clamp member suspended from the lever arms. The rear end of the screen is suspended from the frame by turnbuckles which allow the position of the screen to be manually adjusted.

United States Patent 1191 Fuchs 1451 Aug. 13, 1974 SQUEEGEE AND FLOOD BAR ACTUATOR WITH PEELING SCREEN CLAMP [75] Inventor: Alvin J. Fuchs, Milwaukee, Wis.

[73] Assignee: Medalist Industries, Inc.,

Milwaukee, Wis.

22 Filed: Nov. 16, 1972 211 Appl.No.:307,322

[52] US. Cl. 101/123, 101/127.1 [51] Int. Cl. B4lt 15/36, B4lf 15/42 [58] Field of Search 101/114, 123, 124, 126,

[56] References Cited UNlTED STATES PATENTS 10/19-35 Wulf 101/123 X 12/1936 Wulf.... l0l/l26 Primary Examiner-Robert E. Pulfrey Assistant ExaminerR. E. Suter Attorney, Agent, or FirmWheeler, Morsell, House & Fuller [5 7] ABSTRACT The squeegee and flood bar assemblies of a screen printing machine are reciprocally moved along a spaced pair of parallel rails to alternately effect a printing stroke and a flood stroke. The rails are part of a frame which is pivoted for tilting movement between a printing position and a flood position. The squeegee assembly is slideably engaged in a third rail or control rail which is raised and lowered in coordination with the movement of the frame to lower the squeegee into contact with the printing screen at the start of the printing stroke and to raise it above the screen at the start of the flood stroke. The flood bar assembly is linked to the squeegee assembly to raise the flood bar when the squeegee is lowered and to lower the flood bar when the squeegee is raised. The front end of the printing screen is held in a clamp which is suspended below the parallel rails and includes a rod rotatably attached to the frame along an axis which is transverse to the rails, a pair of spaced lever arms projecting from the rod, and a linear clamp member suspended from the lever arms. The rear end of the screen is suspended from the frame by turnbuckles which allow the position of the screen to be manually adjusted.

16 Claims, 8 Drawing Figures PATENTEU mm 3:974

SHEU 2 1F 4 SQUEEGEE AND FLOOD BAR ACTUATOR WITH PEELING SCREEN CLAMP BACKGROUND OF THE INVENTION This invention relates to screen printing machines in which pictures, shapes, forms, or letters to be printed are defined on a silk or nylon screen by making a correspondingly shaped portion of the screen permeable with respect to printing ink while the remaining portions of the screen are impermeable. A relatively heavy ink is deposited on one side of the screen and the other side of the screen is placed adjacent to the surface which is to be printed upon. A squeegee is then moved across the inked side of the screen to force the ink through the permeable portion of the screen and onto the surface to be printed upon. The printed surface is then removed and replaced by a fresh surface while, at the same time, the deposit of ink is moved back to its starting point by pushing it across the screen with a flood bar.

In automatic screen printing machines, such as disclosed in my U.S. Pat. No. 3,263,603, the squeegee and flood bars are commonly mounted on reciprocating carriages which move back and forth over the inked side of the screen, the squeegee being lowered into contact with the screen before the printing stroke, and being raised off the screen before the flood stroke, while the flood bar is lowered before the flood stroke and raised before the printing stroke. The printing frame, which includes a clamp for holding the printing screen and a pair of rails along which the squeegee and flood bar carriages reciprocate, is lowered into contact with the surface to be printed upon at the start of the printing stroke, and is raised off the surface at the start of the flood stroke. This invention is particularly concerned with improvements in the means for supporting and reciprocating the squeegee and flood bar and also in the means for supporting the printing screen.

In the above-noted prior art machines, the connecting rods which reciprocate the squeegee and flood bar carriages are coupled to the carriages, through pivoted crank plates that move the flood bar and squeegee up or down automatically when the direction of the, stroke is changed. One disadvantage of the prior art is that this connection has a tendency to allow the flood bar to lift accidentally toward the end of the flood stroke. As the speed of the carriages is reduced at the end of the flood stroke, the momentum due to the weightof the squeegee assembly urges it to move faster than the flood bar, which pulls the flood bar up prematurely, and leaves a heavy deposit of ink at that point and a dry space becarriages, the connecting rods are already in motion, and this causes the carriages to start moving in an abrupt or jerky manner that tends to cause skip printing at the start of the printing stroke. In accordance with this invention, both of the abovenoted problems have been overcome by providing a novel squeegee and flood bar supporting structure in which the couplings or connecting rods that move the squeegee and flood bar carriages are attached directly to the carriages, and in which the upward and downward movement of the squeegee and flood bar are derived from a third rail or control rail which is moved in coordination with movements of the printing frame. These improvements insure a positive downward pressure on the flood bar throughout the flood stroke and also insure a smooth start on the printing stroke.

Another problem in the priorart machines relates to v the means for securing the printing screen to the printyond. This results in insufficient ink at the leading edge of the screen and causes skip printing.

Another disadvantage of the prior art is that at the end of the flood stroke, when the force on the connecting rods is reversed to start the printing stroke, the initial movement of the rods in the reverse direction does not move the carriages but rather causes a rotation of ing frame. The printing screen is usually stretched across a wooden frame which is subject to warpage. In the prior art machines, the wooden frame is supported by a clamp that is loosely suspended by hooks from the front of the printing frame. This loose suspension is provided to allow the screen frame to be lifted slightly during the printing stroke by a spring-loaded plunger to raise the screen off the printing surface immediately after the squeegee passes over it. This keeps the screen from sticking to the printed surface and gives a better quality printing. In some machines, this loose suspension also allows the screen to be moved up and down in connection with a fixed squeegee to make contact with the squeegee at the start of the printing stroke and break contact at the end of the printing stroke. But this loose suspension also allows the position of the screen to be influenced by any warpage that happens to be present in the wooden frame.

In accordance with this invention, however, the effect of warpage has been nullified by means of a linear clamp member which is rotatably attached to the front of the printing frame and which holds the front of the screen frame in correct alignment with the printing table during the printing stroke in spite of warpage. The rotatability of the connection allows the screen frame to lift slightly during the printing stroke to separate it from the printed surface without allowing its position to be influenced by warpage.

SUMMARY OF THE INVENTION A frame including a pair of main rails is pivoted to a base for movement between a lowered printing position and an upwardly inclined flood position. A pair of slide carriages are mounted for reciprocal movement along the rails and a squeegee assembly and flood bar assembly are both pivotally attached between the slide carriages for movement therewith. A third rail or control rail is attached to the frame parallel to the main rails and is moved upwardly and downwardly with respect to the screen and the main rails in coordination with the movement of the frame between its two positions. The squeegee assembly is slideably attached to the control rail to move the squeegee downward before the start of the printing stroke and upward at the end of the printing stroke. Linkage means is connected between the squeegee assembly andflood bar assembly to raise the flood bar when the squeegee is lowered and to lower the flood bar when the squeegee is raised. The front end of the printing screen is attached to the frame by means of a relatively long clamp which is pivotally suspended from a pair of lever arms which project from a rod that is rotatably connected to the frame transverse to the main rails. The rear end of the printing screen is suspended from the frame by turnbuckles which allow the position of the screen to be manually adjusted.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary longitudinal-sectional view of a screen printing machine utilizing one illustrative embodiment of this invention with the printing frame thereof lifted above the printing table and the flood bar lowered to move ink across the printing screen in the flood stroke thereacross. I

FIG. 2 is a fragmentary longitudinal-sectional view of the screen printing machine shown in FIG. 1 with the printing frame thereof lowered into contact with the printing table and the squeegee thereof in contact with the printing screen during the printing stroke thereacross.

FIG. 3 is a fragmentary perspective view showing the upper front portions of the squeegee and flood bar supporting structure of the embodiment shown in FIGS. 1 and 2 and the front screen frame clamp therefor.

FIG. 4 is a fragmentary detailed perspective view of one corner of the front screen frame clamp shown in FIG. 3.

FIG. 5 is a fragmentary cross-sectional view of the embodiment shown in FIGS. 1-4 with portions of the squeegee assembly cut away to expose the flood bar assembly.

FIG. 6 is a fragmentary detail longitudinal-sectional view of the front screen frame clamp and the spring loaded plunger which raises the screen after printing.

FIG. 7 is a fragmentary plan view of the rear corners of the printing frame and its supporting structure.

FIG. 8 is a fragmentary detail view of the other corner of the front screen frame clamp shown in FIGS. 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. The scope of the invention is defined in the claims appended hereto.

Referring to FIGS. 1, 2 and 7, one illustrative embodiment of this invention is shown mounted on an automatic screen printing machine which is supported by base members l0, l2 and other suitable supporting elements including legs which are not shown in the drawings. The base members l0, 12 et. al., support a rectangular printing table 14 which has a perforated top and is coupled to a source of vacuum so as to hold sheet material to be printed firmly on the top of the table as is conventional in the screen printing art. A pair of base extension members 16 are attached to the rear of the base members and 12 at opposite sides of the base and extend rearwardly therefrom. A rectangular printing frame 18 is pivotally connected to the base members 16 by bolts 20 and is movable between a printing position which is shown in FIG. 2 and a flood position which is shown in FIG. 1. The means for moving the printing frame up and down between its two positions does not have any bearing upon the instant improvements and hence this means is not shown in the drawings. It can be the same as disclosed in my US. Pat. No. 3,263,603 where a rotating cam 43 and its associated parts cause a similar printing frame to be alternately raised and lowered.

The printing frame 18 is rectangular in plan and includes laterally spaced side members 22, front and rear cross members 24, and upright post members 26 at the rear corners of the frame, all 'of which are joined together in a conventional manner to provide a rigid framework for supporting a pair of parallel rails 28, one at each side of the frame. The rails 28 each have an inwardly facing recessed slide track 30 formed therein for slideably supporting a reciprocable squeegee and flood bar assembly to be described later. The rails 28 are supported at their rear ends on the carrier posts 26 and are joinedtogether at their swinging front ends by a cross handle bar 32 which is rigidly attached between the two rails 28 as shown in'FIGS. 2, 3 and 4. A printing screen comprising a rectangular wooden framework 34 over which a flexible silk or nylon screen 35 is stretched is suspended below the rails 28 by clamping means described below.

One of the problems that this invention is concerned with is the effect of warpage in the wooden frames 34 that support'the printing screen 35. It is necessary to suspend the printing frame 34 loosely enough from the rails 28 at its front edge so that the screen 35 may be raised slightly after the printing squeegee passes over it, thus to immediately separate the screen from the printed area underneath it during the printing stroke. In machines which have a fixed squeegee, this loose suspension is also necessary to allow the screen to be raised to make contact with the squeegee at thestart of the printing stroke and to be lowered to break contact with the squeegee at the end of the printing stroke. In the past, this necessity for a loose suspension has led to clamping arrangements in which warpage in the wooden frame 34 was allowed to affect the position of the printing screen relative to the printing table. In accordance with this invention, however, an improved clamping means has been provided in which the effect of warpage is nullified without restricting the slight movement of the frame which is necessary to lift the screen after printing. The rear edge of printing frame 34 is suspended in an adjustable clamp described below.

Referring to FIGS. 1 and 2, the rear end cross rail 33 of the printing frame 34 is clamped in a linear C-shaped rear clamp 36 by clamping screws 38. The rear clamp 36 is adjustably secured to the printing frame by two pairs of turnbuckles 40 and 44, each pair being attached to a projecting ear 42, one on each end of the clamp member 36. The corresponding turnbuckles 40 provide horizontal adjustability for the clamp member 36 and the corresponding turnbuckles 44 provide vertical adjustability. As shown in FIG. 3, a relatively long turnbuckle 46 is attached at 47 between the center of clamp member 36 and the printing frame 18 to provide lateral adjustability for the clamp 36. Accordingly, the rear end of printing frame 34 floats in an adjustable suspension formed by the turnbuckles 40, 44 and 46.

A front clamp for the screen frame 34 includes a linear C-shaped clamp member 48 within which the front end cross rail 37 of screen frame 34 is secured by thumb screws 50 (see FIG. 4). The front clamp 48 is pivotally suspended by links 52 from lever arms 54 that are rigidly attached to a rod 56 and project rearwardly therefrom. The rod 56 is rotatably suspended below the handle 32 through openings in ears 58 attached thereto (see FIG. 3). As shown in FIGS. 3 and 4, one of the lever arms 54 has a forwardly and upwardly projecting lug 55 that faces the front edge of cross handle bar 32 and abuts against the end of a set screw 57 that extends through cross handle bar 32. Lug 55 rotates with rod 56 and when it abuts against set screw 57 it limits the downward movement of lever arms 54. Thus set screw 57 provides an adjustable lower limit for the position of clamp 48 relative to cross handle bar 32.

As shown in FIG. 8, one end of rod 56 is transversely adjustably attached to the corresponding ear 58 via a bolt 152 which passes through an opening in ear 58 and engages a threaded opening in a collar 153 which is rigidly attached to the end of rod 56. A nut 154 is engaged in the threaded portion of bolt 152 adjacent to collar 153 to act as a lock nut. A fixed sleeve 156 is rigidly attached to the shank of bolt 152 on the side of ear 58 opposite the head of bolt 152, and a nylon bearing sleeve 157 is mounted around the shank of bolt 152 where it passes through ear 58. By means of this mounting, the clamp member may be adjusted transversely as follows. First the nut 154 is loosened, then bolt 152 is turned clockwise to move rod 56 and frame 37 to the left in FIG. 8 or counterclockwise to move rod 56 and frame 37 to the right in FIG. 8. When the desired position is arrived at, nut 154 is retightened. While this transverse adjustment is being accomplished, a compression spring 60 at the other end of rod 56 (see FIG. 3) holds the bearing sleeve for the other ear 58 in place in spite of the transverse movement.

A spring-loaded retractable frame support foot or plunger 62 is slideably mounted within a collar 64 to the front of clamp member 48 (see FIGS. -3 and 6). Foot 62 is normally extended downwardly by two springs 66 attached at opposite ends of a cross pin 68 that passes through the upper end of foot 62. When the printing frame is lowered into its printing position, as shown in FIG. 2, the extended spring biased support foot 62 contacts the top of table 14 (see FIG. 6) and normally holds the front cross rail 37 of printing frame 34 up off the surface of the table by a predetermined amount. When the squeegee is pressed down against the front end of the screen 35, the foot 62 yields and retracts upwardly as the front cross rail 37 is moved downwardly by the pressure of the squeegee until the flexible screen 35 is in contact with the surface to be printed upon. As the printing stroke commences, however, and the squeegee moves from the front toward the rear of the screen frame 34, the flexibility of the screen 35 relieves the frame of the down pressure of the squeegee and the spring pressure on the foot 62 lifts the clamp 48, thereby lifting the front cross rail 37 and lifting the portions of the screen 35 previously traversed by the squeegee out of contact with the printed surface as the squeegee moves along. This slight lifting of the front cross rail 37 is permitted by the rotary connection between rod 56 and the handle 32 and by the pivotal suspension of the clamp 48 from the rod 56.

The relatively long length of the clamp member 48 and the positive downward pressure of the thumb screws 50 holds the front cross rail 37 in accurate linear alignment with printing table 14 in spite of any warpage therein and the rotary mounting of the rod 56 insures that the front edge of screen 35 is free to move upwardly under the urging of foot 62 as the squeegee moves from the front to the rear of the screen. The transverse position of the front clamp member 48 can be adjusted as described above with the bolt 152 to register the position of the printing screen.

This invention is also concerned with improvements in the means for supporting and reciprocating the squeegee assembly and flood bar assembly over the printing screen 35 to overcome the skip printing problem discussed above. As shown in FIG. 2, in the print ing position of printing frame 18, the squeegee assembly includes a resilient squeegee 70 which is mounted in a wooden squeegee block 72. Squeegee 70 is lowered into contact with the printing screen 35 and is moved rearwardly in the printing stroke in the direction of arrow 73 across the upper surface of the printing screen 35 to force printing ink 74 through the permeable areas of screen 35 and onto a sheet which is supported on table 14 below the printing screen 35. At the end of this printing stroke, the squeegee 70 is raised from the surface of the printing screen 35 and a flood bar 76, which is mounted in a flood bar block 78 as part of the flood bar assembly, is lowered into contact with the printing ink 74 as shown in FIG. 1. The flood bar 76 is then moved forwardly in the flood stroke in the direction of arrow 75 across the printing screen 35 from its rear edge towards its front edge to move the ink 74 back to the front edge of the screen 35 in preparation for the next printing stroke. These reciprocal movements of the squeegee 70 and the flood bar 76 are obtained by reciprocally driving a pair of slide carriages 80 which are slideably engaged in the tracks 30 of rails 28 on opposite sides of the screen printing machine by means of nylon slides 81 (see FIG. 5). The carriages 80 are reciprocally driven by a pair of connecting rods 82 which are pivotally attached to the slide carriages 80 at 84. Since this invention is not concerned per se with the reciprocal drive means for connecting rods 82, it is not shown in the drawings, and any conventional means can be employed to perform the reciprocal drive function, as disclosed, for example, in the above-noted US. Pat. No. 3,263,603, where the reciprocal drive function is initiated by a rotating linkage arm 70 and coupled to the slide carriages by connecting rods 68.

The squeegee block 72 is secured in a clamp member 86 and is locked therewithin by means of two thumb screws 88. A swivel bar 90 is pivotally attached to the top of the clamp 86 by end brackets 92 (see FIG. 3)

and the angle between the swivel bar 90 and the clamp- 86 is adjustable by means of adjustment screws 94. The swivel bar 90 is attached by threaded studs 96 to a squeegee cross bar 98. The studs extend through the squeegee cross bar 98 and are adjusted by hand wheels 100 (see FIG. 3) which control the spacing of squeegee 70 with respect to printing screen 35. The squeegee cross bar 98 is pivotally attached to and spans between the two slide carriages 80 through plates 102 which are rigidly connected to opposite ends of cross bar 98 and pivotally connected at 104 to the corresponding slide carriage 80. Squeegee cross bar 98 is also engaged by means for pivoting the plates 102 about their trunnions 104 so as to raise and lower the squeegee 70 with respect to printing screen 35 as will be described hereinafter.

Before describing the means which raise and lower the squeegee 70, it will be expedient to first describe the mounting for the flood bar 76 and the linkage between the flood bar supporting structure and the squeegee supporting structure. The flood bar 76 is held in a flood block 78 which is secured by studs 106 to a flood bar cross bar 108. The studs 106 extend through flood cross bar 108 and are secured by hand wheels 110 (see FIG. 3) through which the position of the flood bar- 76 with respect to printing screen 35 can be manually adjusted. Flood cross bar 108 is pivotally connected at its opposite ends to the slide carriages 80 by means of levers 112 which are rigidly connected to opposite ends of flood bar 108 and pivotally connected on pintles 114 to the corresponding slide carriage 80. Because of this pivotal mounting, the flood cross bar 108 can be moved upwardly and downwardly to move the flood bar 76 upwardly and downwardly with respect to printing screen 35.

When the squeegee 70 is moved downwardly into contact with printing screen 35, the flood bar 76 is concurrently moved up away from the screen 35, as shown in FIG. 2, and when the squeegee 70 is moved away from the printing screen 35, the flood bar 76 is concurrently moved downward toward the printing screen 35. This action is obtained by means of a centrally located coupling or linkage between the flood cross bar 108 and the squeegee cross bar 98, which linkage or coupling includes a lever 116 rigidly attached to the center of flood cross bar 108, a lever 118 rigidly attached to the center of squeegee cross bar 98, and an intermediate link 120 which is pivotally connected between levers 116 and 118 by pintle pins .122 and 124. This linkage acts to raise flood bar 76 when squeegee 70 is lowered and to lower flood bar 76 when squeegee 70 is raised. It is most clearly shown in FIGS. 1 and 3. Referring to FIG. 1, when squeegee 70 is lowered by lowering squeegee cross bar 98, lever 118 is moved both rearwardly and downwardly due to the rotation of plates 102 about trunnions 104. This pulls link 120 and lever 116 rearwardly, which causes flood cross bar 108 and levers 112 to pivot upwardly aboutv pintles 114, thereby raising flood bar 76, when squeegee 70 is lowered. When squeegee cross bar 98 is raised to raise squeegee 70, lever 118 is moved both forwardly and upwardly due to the rotation of plates 102 about trunnions 104. The forward component of motion pulls link 120 and lever 116 forwardly, which causes flood cross bar 108 and levers 112 to pivot downwardly about pintles 114, thereby lowering flood bar 76 when squeegee 70 is raised.

The upward and downward movement of squeegee 70 and flood bar 76 with respect to screen 35 is sychronized with the up and down movement of the printing frame 18 with respect to table 14 so that the squeegee 70 will move down into contact with the printing screen 35 at the start of the printing stroke, and the flood bar 76 will move downwardly into contact with the ink 74 at the start of the flood stroke. In accordance with this invention, this synchronism is accomplished by means of a single third rail or control rail 126 which is mounted above one of the main rails 28 by a pivoted parallelogram linkage that requires the third rail 126 to be moved upwardly and downwardly with respect to the main rail 28 below it, while remaining parallel with the same. The third rail 126 has an inwardly facing recessed slide track 128. A slide element, such as a bracket or carriage 130, is connected to either the squeegee assembly or the flood bar assembly. In the illustrated embodiment carriage 130 is rigidly attached at one end to the squeegee cross bar 98 and is continuously slideably engaged at its other end in the slide track 128 via a nylon slide 131. Third rail 126 is parallel with main rails 28. Therefore, regardless of the position of squeegee cross bar 98 along the main rails28, cross bar 98 can be moved in synchronism with the upward and downward movements of the third rail 126 by the force transmitted by the rail 126 to bar 98 through the slide bracket 130 and its slide 131.

Downward movement of the third rail 126 causes a downward pivoting of the squeegee cross bar 98 and a consequent downward movement of the squeegee 70. Upward movement of the third rail 126 causes an upward pivoting of the squeegee cross bar 98 and a corresponding upward movement of the squeegee 70. These upward and downward movements of the squeegee are translated through the linkage members 116 118 and into reverse movements of the flood bar 76 as explained previously.

The third rail 126 is actuated in a parallelogram motion to swing between its raised position shown in FIG. 1 and its lowered position shown in FIG. 2. At its front end, third rail 126 is pivotally linked to the front end of the main rail 28 below it by means of a curved linkage arm 132 (see FIGS. 1 and 3) which is pivotally connected to third rail 126 by pintle pin 134 and is pivotally connected to main rail 28-by pintle pin 136. At its rear end (see FIGS. 1 and 2) the third rail 126 is pivotally connected by a pintle pin 138 to a linkage arm 140 which is also pivotally connected by pin 142 to support pad 141 which is attached to main rail 28. Linkage arms 132 and 140 are effectively parallel to each other to effect a parallelogram motion of third rail 126 with respect to the adjacent main rail 28 and screen 35.

Linkage arms 132 and 140 are effectively parallel with each other because a line drawn through the centers of pivot pins 134 and 136 of arm 132 is parallel with a line drawn through the centers of pivot pins 138 and 142 of arm 140. Accordingly, as far as their effect on the other parts of the structure is concerned, arms 132 and 140 act as parallel linkages even though because of their configurations they are not strictly parallel.

The rear linkage arm 140 extends beyond thepintle pin 142 and is pivotally connected by pintle pin 144 to a two piece or bent connecting rod which comprises two connecting rod members 146 and 148 which are welded together at an angle in order to avoid striking another part of the mechanism which is not shown in the drawing. Connecting rod 148 functions as an actuator for the parallelogram linkages and is pivotally connected at its lower end by a pintle bolt 150 to the base member 10. Therefore, when the printing frame 18 is lifted to its flood position, shown in FIG. 1, the forces communicated through the connecting rods 146 and 148 to the linkage arm 140 cause the arm 140 to pivot clockwise about its pintle 142 and the third rail 126 to be raised above the main rail 28. This causes the squeegee 70 to be raised and concurrently lowers the flood bar 76 into contact with the screen 35 and ink .74 in preparation for a flood stroke. When the printing frame 18 is moved to its printing position, shown in FIG. 2, the linkage arm 140 is pivoted counterclockwise about its pintle 142 by the forces applied through connecting rods 146 and 148, thus to lower the third rail 126 with respect to the main rail 28. This lowers the squeegee 70 into contact with the printing screen 35 and concurrently raises the flood bar 76 away from the printing screen 35 in preparation for a printing stroke.

In the apparatus of this invention, positive downward pressure is maintained by third rail 126 on the flood bar 76 throughout the entire flood stroke so that there is no tendency for the flood bar to raise as the slide carriages 80 slow down at the end of the stroke. Also, since the connecting rods 82 which move the slide carriages 80 are connected directly to the slide carriages, there is no tendency for the slide carriages to start in an abrupt or jerky manner at the beginning of the printing stroke as there was in the prior art structures. Instead, the carriages 80 come to a smooth stop at the end of the flood stroke and start out equally smoothly at the start of the printing stroke. In addition, the upward and downward movements of squeegee 70 and flood bar 76 are positively synchronized with the upward and downward movements of the printing frame 18 so that the squeegee 70 and flood bar 76 will be in their proper position at the start of the printing stroke and the flood stroke.

Although the foregoing disclosure describes one embodiment of the invention in detail, it should be understood that this invention is not limited to the disclosed embodiment since many modifications can be made in the disclosed structure without departing from the basic principles of this invention. For example, instead of slideably engaging the squeegee cross bar 98 in the third rail 126 to move the squeegee up and down in coordination with the movements of the third rail, it is possible to slideably engage the flood cross bar 108 in the third rail 126 and to derive the movements of the squeegee from the movements. of the flood bar. This would require that the pivot point for the linkage arms moving the third rail up and down be moved so as to reverse the upward and downward movement of third rail. Such changes would not, however, depart from the basic principle of this invention, which is to derive the upward and downward movements of the squeegee and flood bar from movements of the third rail. Similar modifications will be apparent to those skilled in the art, and this inventionincludes all such modifications as may fall within the scope of the following claims.

I claim:

1. In a screen printer, the combination comprising a base, a printing frame pivoted to said base for movement between a printing position and flood position, said frame including a pair of main rails which extend substantially parallel to each other and means for supporting a printing screen below said rails, a first slide carriage slideably engaged with one of said rails and movable therealong, a second slide carriage slideably engaged with the other rail and movable therealong, means for reciprocally moving said slide carriages along said rails back and forth between opposite ends of said printing screen, a squeegee assembly mounted between said slide carriages for movement therewith along said rails, said squeegee assembly including means for supporting a squeegee above said printing screen, a flood bar assembly mounted between said slide carriages adjacent to said squeegee assembly, said flood bar assembly including means for supporting a flood bar above said printing screen, linkage means connected between said squeegee assembly and said flood bar assembly for raising the flood bar when the squeegee is lowered and lowering the flood bar when the squeegee is raised, a control rail mounted on said printing frame and movable toward and away from said printing screen, a slide element slideably engaged with said control rail and movable therealong, means connecting said slide element to one of said assemblies for raising and lowering the same, and means for moving said control rail in one direction when said frame is moved into its printing position to lower said squeegee into contact with said printing screen and to raise said flood bar away from the same, and for moving said control rail in another direction when said frame is moved into its flood position as to raise said squeegee away from said printing screen and lower said flood bar toward the same.

2. A screen printer as defined in claim 1 wherein said control rail is mounted on said printing frame by a pivoted parallelogram linkage including a pair of parallel linkage arms pivotally connected between opposite ends of said control rail and said printing frame, and wherein the means for moving said control rail comprises means coupling one of said linkage arms to said base at such angle that said control rail will be raised and lowered by movement of said one linkage arm as said printing frame is moved between its two positions.

3. A screen printer as defined in claim 1 wherein said control rail is mounted substantially parallel with said main rails.

4. A screen printer as defined in claim 1 wherein said squeegee assembly is pivotally connected to said slide carriages and said flood bar assembly is pivotally connected to said slide carriages, and wherein said linkage means connected between said squeegee assembly and said flood bar assembly comprises a first lever arm rigidly attached to said squeegee assembly and projecting therefrom, a second lever arm rigidly attached to said flood bar assembly and projecting therefrom, and a link pivotally connected at one end to said first lever arm and pivotally connected at its other end to said second lever arm.

5. A screen printer as defined in claim 1 wherein said means for reciprocably moving said slide carriages is pivotally connected directly to said slide carriages to communicate the force for said movement directly to said slide carriages.

6. A screen printer as defined in claim 2 wherein said means coupling said one linkage arm to said base comprises a connecting rod pivotally connected between said base and one end of said one linkage arm.

7. A screen printer as defined in claim 1 wherein said means for supporting a printing screen includes a rod rotatably attached to said frame along an axis which is transverse to said rails, a pair of lever arms rigidly attached to said rod and projecting from said rod at spaced apart locations therealong, a linear clamp member pivotally attached to said lever arms and suspended thereby below the level of said rod, said clamp member being shaped to receive one framing member of said printing screen and including means for clamping said framing member within said clamp member.

8. An improved clamping means as defined in claim 7 and further comprising a second clamp member shaped to receive asecond framing member of said printing screen and including means for clamping said second framing member within said second clamp member, and means for suspending said second clamp member from said printing frame opposite the first frame pivoted to said base for movement between a printing position and a flood position, an improved clamping means for securing a printing screen to said frame comprising a rod rotatably attached to said frame, a pair of lever arms rigidly attached to said rod and projecting from said rod at spaced apart locations therealong, a linear clamp member pivotally attached to said lever arms and suspended thereby below the level of said rod, said clamp member being shaped to receive one framing member of said printing screen and including means for clamping said framing member within said clamp member.

1 1. An improved clamping means as defined in claim 10 wherein said printing screen has a front and a rear framing member and wherein said clamp member is positioned to receive the front framing member and further comprising a foot member movably attached to said clamp member and extending downwardly therefrom, said foot member being spring loaded to urge said clamp member upwardly,'thereby urging the front edge of said printing screen upwardly to separate the screen from the printed surface below it during the printing operation.

12. An improved clamping means as defined in claim 10 wherein said rod is adjustably attached to said frame.

13. An improved clamping means as defined in claim 10 and further comprising means for adjustably limiting the rotation of said rod.

14. In a screen printer having a screen, a squeegee and a flood bar, reciprocating means for moving said squeegee and flood bar forth and back along said screen, a track for guiding the movement of the reciprocating means and actuating means for engaging one of said squeegee and flood bar with the screen and withdrawing the other of said squeegee and flood bar from the screen at the beginning of said forth and back movements, the improvement in which said actuating means comprises a control rail, a slide engaged with and movable along said control rail for continuous contact therewith, couplings respectively between said slide and said squeegee and flood bar, and means for moving said control rail toward and away from said screen.

15. The invention of claim 14 in which said means for moving said third rail comprises parallelogram linkages and an actuator therefor.

16. The invention of claim 15 in which said reciprocating means alternates between a flood stroke and a printing stroke, and in which said reciprocating means is mounted upon a tilting frame which is tilted to an upwardly tilted position above a printing table between the printing stroke and the flood stroke and is tilted to a lowered position adjacent to said printing table between the flood stroke and the printing stroke, said actuator comprises a link pivotally connecting one of said parallelogram linkages to said printing table. 

1. In a screen printer, the combination comprising a base, a printing frame pivoted to said base for movement between a printing position and flood position, said frame including a pair of main rails which extend substantially parallel to each other and means for supporting a printing screen below said rails, a first slide carriage slideably engaged with one of said rails and movable therealong, a second slide carriage slideably engaged with the other rail and movable therealong, means for reciprocally moving said slide carriages along said rails back and forth between opposite ends of said printing screen, a squeegee assembly mounted between said slide carriages for movement therewith along said rails, said squeegee assembly including means for supporting a squeegee above said printing screen, a flood bar assembly mounted between said slide carriages adjacent to said squeegee assembly, said flood bar assembly including means for supporting a flood bar above said printing screen, linkage means connected between said squeegee assembly and said flood bar assembly for raising the flood bar when the squeegee is lowered and lowering the flood bar when the squeegee is raised, a control rail mounted on said printing frame and movable toward and away from said printing screen, a slide element slideably engaged with said control rail and movable therealong, means connecting said slide element to one of said assemblies for raising and lowering the same, and means for moving said control rail in one direction when said frame is moved into its printing position to lower said squeegee into contact with said printing screen and to raise said flood bar away from the same, and for moving said control rail in another direction when said frame is moved into its flood position as to raise said squeegee away from said printing screen and lower said flood bar toward the same.
 2. A screen printer as defined in claim 1 wherein said control rail is mounted on said printing frame by a pivoted parallelogram linkage including a pair of parallel linkage arms pivotally connected between opposite ends of said control rail and said printing frame, and wherein the means for moving said control rail comprises means coupling one of said linkage arms to said base at such angle that said control rail will be raised and lowered by movement of said one linkage arm as said printing frame is moved between its two positions.
 3. A screen printer as defined in claim 1 wherein said control rail is mounted substantially parallel with said main rails.
 4. A screen printer as defined in claim 1 wherein said squeegee assembly is pivotally connected to said slide carriages and said flood bar assembly is pivotally connected to said slide carriages, and wherein said linkage means connected between said squeegee assembly and said flood bar assembly comprises a first lever arm rigidly attached to said squeegee assembly and projecting therefrom, a second lever arm rigidly attached to said flood bar assembly and projecting therefrom, and a link pivotally connected at one end to said first lever arm and pivotally connected at its other end to said second lever arm.
 5. A screen printer as defined in claim 1 wherein said means for reciprocably moving said slide carriages is pivotally connected directly to said slide carriages to communicate the force for said movement directly to said slide carriages.
 6. A screen printer as defined in claim 2 wherein said means coupling said one linkage arm to said base comprises a connecting rod pivotally connected between said base and one end of said one linkage arm.
 7. A screen printer as defined in claim 1 wherein said means for supporting a printing screen includes a rod rotatably attached to said frame along an axis which is transverse to said rails, a pair of lever arms rigidly attached to said rod and projecting from said rod at spaced apart locations therealong, a linear clamp member pivotally attached to said lever arms and suspended thereby below the level of said rod, said clamp member being shaped to receive one framing member of said printing screen and including means for clamping said framing member within said clamp member.
 8. An improved clamping means as defined in claim 7 and further comprising a second clamp member shaped to receive a second framing member of said printing screen and including means for clamping said second framing member within said second clamp member, and means for suspending said second clamp member from said printing frame opposite the first mentioned clamp member and for vertically adjusting the position of said second clamp member relative to said printing frame.
 9. An improved clamping means as defined in claim 8 wherein said second clamp member is suspended from said printing screen by a pair of substantially vertically oriented turnbuckles which are connected between said printing frame and said second clamp member to support said second clamp member and adjust its vertical position relative to said printing frame.
 10. In a screen printer having a base and a printing frame pivoted to said base for movement between a printing position and a flood position, an improved clamping means for securing a printing screen to said frame comprising a rod rotatably attached to said frame, a pair of lever arms rigidly attached to said rod and projecting from said rod at spaced apart locations therealong, a linear clamp member pivotally attached to said lever arms and suspended thereby below the level of said rod, said clamp member being shaped to receive one framing member of said printing screen and including means for clamping said framing member within said clamp member.
 11. An improved clamping means as defined in claim 10 wherein said printing screen has a front and a rear framing member and wherein said clamp member is positioned to receive the front framing member and further comprising a foot member movably attached to said clamp member and extending downwardly therefrom, said foot member being spring loaded to urge said clamp member upwardly, thereby urging the front edge of said printing screen upwardly to separate the screen from the printed surface below it during the printing operation.
 12. An improved clamping means as defined in claim 10 wherein said rod is adjustably attached to said frame.
 13. An improved clamping means as defined in claim 10 and further comprising means for adjustably limiting the rotation of said rod.
 14. In a screen printer having a screen, a squeegee and a flood bar, reciprocating means for moving said squeegee and flood bar forth and back along said screen, a track for guiding the movement of the reciprocating means and actuating means for engaging one of said squeegee and flood bar with the screen and withdrawing the other of said squeegee and flood bar from the screen at the beginning of said forth and back movements, the improvement in which said actuating means comprises a control rail, a slide engaged with and movable along said control rail for continuous contact therewith, couplings respectively between said slide and said squeegee and flood bar, and means for moving said control rail toward and away from said screen.
 15. The invention of claim 14 in which said means for moving said third rail comprises parallelogram linkages and an actuator therefor.
 16. The invention of claim 15 in which said reciprocating means alternates between a flood stroke and a printing stroke, and in which said reciprocating means is mounted upon a tilting frame which is tilted to an upwardly tilted position above a printing table between the printing stroke and the flood stroke and is tilted to a lowered position adjacent to said printing table between the flood stroke and the printing stroke, said actuator comprises a link pivotally connecting one of said parallelogram linkages to said printing table. 